The present invention relates to fans, mainly to axial-flow fans, and more particularly to the impeller of an axial-flow fan.
1. Field Of The Invention
The present invention can be used most successfully in large high-efficiency fans designed, say, for flue gas extraction, for venting mines, in cooling towers and in other cases calling for the creation of powerful gas streams.
2. Prior Art
Known in the prior art is a great number of various designs of impellers of axial-flow fans. Commonly known in current technology are the impellers of axial-flow fans comprising a hub provided with variable-incidence blades arranged at a constant pitch. One of the disadvantages of such an impeller is that it requires the use of blades with a complex profile. In view of insufficient vibration strength of the plate-profile blades, the latter have found little use in axial fan impellers with blades spaced at a constant pitch.
In another design of impellers also known in the prior art the impeller comprises a hub provided with variable-incidence blades spaced at a varying pitch which gradually grows to a certain preset value, then the whole cycle is repeated over again.
In both cases described above, each blade has an individual means for fastening it to the impeller hub.
The hollow impeller blades with a complex profile possess a number of disadvantages; firstly, when the surface of the blades is corroded to the point of development of through holes, this may cause penetration of dust and moisture into the blades, thus putting the impeller out of balance; secondly, such blades are difficult to make and in many cases this requires the use of manual labor; thirdly, the complexity of manufacture raises the cost of such blades; and finally, it is difficult to ensure automatic turning of such blades, because each blade must be turned individually and has an attachment fiting of its own.